Explain repeat {} while/until block

Closes #688

doc/Language/control.pod6

@@ -670,26 +670,15 @@ All these forms may produce a return value the same way C<loop> does.
 
 =head1 X<repeat/while, repeat/until|control flow,repeat>
 
-Perl 5 allows one to apply a statement modifier to a C<do> block such that
-C-like constructs such as
-
-    do {
-        ...
-    } while $x < 10;   # allowed in Perl 5; not in Perl 6
-
-are possible.
-
-This is specifically disallowed in Perl 6.  Nevertheless, one can repeat a
-block up to a given condition in the same way with a C<repeat> loop:
+Executes the block I<at least once> and, if the condition allows, repeats
+that execution.
 
     repeat {
-        ...
+        # Execute this block. Then, execute it again and again, until $x >= 10
     } while $x < 10;
 
-This can also be written quite naturally with C<until>:
-
     repeat {
-        ...
+        # Execute this block. Then, execute it again and again, while $x < 10
     } until $x >= 10;
 
 All these forms may produce a return value the same way C<loop> does.